It is well known that during well drilling operations, drillstring assemblies can undergo potentially damaging vibrations. Axial (e.g. bit bounce), torsional (e.g. stick-slip), and lateral (e.g. flexing, whirling) vibrations are well known phenomena that can damage drilling assemblies. See Jardine S., Malone, D., and Sheppard, M., “Putting a damper on drilling's bad vibrations,” THE OILFIELD REVIEW, Schlumberger, January 1994. Extensive study and engineering has been done over the years to better understand, monitor, and control these potentially damaging drillstring vibrations. See Rabia, H., “Oilwell drilling engineering principles and practice,” Graham & Trotman, 1985; Clayer, F., Vandiver, J. K., and Lee, H. Y., “The effect of surface and downhole boundary conditions on the vibration of drillstrings,” PROCEEDINGS 65 ANNUAL TECH. CONF. SPE, New Orleans, SPE 20447 1990; Tucker, R. W. and Wang, C., “An integrated model for drillstring dynamics,” Lancaster University, 2000; Dykstra, M. W., Chen, D. C., Warren, T. M., and Azar, J. J., “Drillstring component mass imbalance: A major source of downhole vibrations,” SPE DRILLING AND COMPLETIONS, December 1996; Lesso W. G. Jr., Chau, M. T., and Lesso, W. G. Sr., “Quantifying bottomhole assembly tendency using field directional drilling data and finite element model,” SPE/IADC 52835, 1999.
Downhole monitoring and surface control techniques have been proposed to deal with some of the vibrations mentioned above. See Halsey G. W., Kyllingstad, A., and Kylling, A., “Torque feedback used to cure slip-stick motion,” SPE 18049, 1988; Alley, S. D. and Sutherland, G. B., “The use of real-time downhole shock measurements to improve BHA component reliability,” SPE 22537 1991; Aldred, W. D., and Sheppard, M. C., “Drillstring vibrations: A new generation mechanism and control strategies,” SPE 24582 1992; Chen, D. C-K., Smith, M., and LaPierre, S., “Integrated drilling dynamics system closes the model-measure-optimize loop in real time,” SPE/IADC 79888. However, it has become clear that in-situ damping of the vibrations would have a greater impact on limiting the extent of damage caused by the vibrations the drillstring is subjected to.
Accordingly, some have proposed in-situ damping techniques, although each has its limitations. APS Technology suggests use of an isolation sub, which includes two loosely threaded cylindrical members with rubber molded into the threaded cavity. The rubber between threaded cylindrical members is intended to damp the drilling induced vibrations. Nevertheless, the temperature-dependent properties of rubber, inter alia, make it difficult or impossible to obtain reliable performance across different drilling conditions. In addition, the huge torque and axial loads common to drilling operations must be transmitted through the rubber damping material, which is difficult. Cobern and Wassell propose a modified sub in which a magnetorheological fluid filling a narrow gap between two components of the drillstring assembly is used as the damping mechanism. Cobern, M. E., and Wassell, M. E., “Drilling vibration monitoring and control system,” APS TECHNOLOGY INC. TECH. REPORT APS-DVMCS, 2004. The viscosity of the fluid is regulated by a magnetic circuit to tune the damping under different drilling conditions. It is not clear, however, that this proposal will be effective.
The present specification is directed to overcoming, or at least reducing the effects of, one or more of the problems outlined above.